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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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Old 04-28-2011, 05:37 AM
ddcc ddcc is offline
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Default Portable UV Water Purifier

I'm currently working on a portable UV water purification project, but am having a little trouble with the UV emission. I've looked into possibly using an ultraviolet LED array, but the problem with this is that most UV LEDs emit the wrong frequency of UV to be germicidal (~400nm, instead of ~250nm). UV fluorescent germicidal bulbs do work, but they require AC power and an additional ballast for constant current, which would require an inverter and controller circuity. Unfortunately, since I'm looking to power this project off of solar cells, I'm trying to keep the excess circuitry to a minimum. Does anyone have any suggestions?
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Old 04-28-2011, 05:56 AM
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marshallf3 marshallf3 is offline
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You're pretty much out of luck, the only decent way to create the proper wavelength of light for germicidal capability is by using a germicidal lamp tube or a laser that operates in that region.

If you can find a very small germicidal lamp tube making a driver circuit to run it off of battery power is easy, matter of fact I've seen entire circuits sold on Goldmine ready to hook up to a tube. One could also salvage the driver circuit out of a fluorescent camping lantern or anything else that runs those little tubes.
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Old 04-28-2011, 06:23 AM
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Since the ballast is just maintaining a constant current despite the decrease in resistivity, would an LED driver work as a substitute, provided that the output voltage was correct?
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Old 04-29-2011, 05:26 AM
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marshallf3 marshallf3 is offline
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Nope, fluorescent tubes need a HV pulse to start ionization of the internal gas then they're current limited to the proper mA for the bulb size, however the voltage across them is still around 85V or whatever it ends up needing to be to maintain the proper current.
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Old 04-29-2011, 08:44 AM
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http://leddev.wordpress.com/2007/11/...he-rest-of-us/
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Old 04-29-2011, 01:29 PM
John P John P is offline
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So how does this gizmo work? Presumably they aren't generating their UV with an LED:
http://www.steripen.com/
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Old 04-29-2011, 09:24 PM
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Although the UV LED's look pretty good, the $300 minimum order is wayyy out of my budget. It looks like the SteriPen does use a regular mercury discharge bulb, located within a quartz sleeve to prevent water contamination if the bulb breaks. The only details that I could find on the electronics are: "SteriPEN uses a fairly straight forward electronic ballast - essentially a Royer Oscillator. The input is nominally 5 Watts with an output of approximately 350VAC RMS @ 40kHz. SteriPEN's electronics are what is termed a regulated power supply. This means that the lamp always gets the same voltage and current or none at all. This means that the lamp will provide the same dose each time rather than going dimmer as a flashlight does when the batteries discharge."
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Old 04-29-2011, 10:22 PM
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I think this thread should be closed. If we advise on this and the water purification fails and the OP dies of dysentery, won't AAC get sued?
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Old 04-30-2011, 03:04 AM
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I believe the onus for 'proving' the proper and safe function of any electronic device is on the person who designs and builds it, not with the party who 'has an idea or suggestion' to give.
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Old 04-30-2011, 04:00 AM
BillO BillO is offline
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I agree with you. Others, not so much.

Sorry to the OP for the hijack.
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